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Sprinkler winterize through back flow preventer test port not working. HELP

This probably has been covered many times but i still see so many opinion. I have a Febco 765 BFP with two test port. I also have a drain valve between Febco and my water supply but nothing after Febco. I tried to blow through lower test port # 2 and it worked at first for 1 zone but but then started making loud sound on second zone (as if pressure is building and no where to release. Then i tried test port 1 and the air was coming from the top of BFP. I took top of BFP out, took out bonnet and puppet and put it back in. Tried again through test port 1 (upper port) and it worked for 2 more zones before air started coming out again from top of 765.

Questions:
(1) which port should i use 1 (upper) and 2 (lower) or drain valve between house main shutoff and BFP.
(2) What the loud sound might be when using port 2? Could i have damaged BFP?
(3) Is it better to blow from drain valve with little bit higher pressure that would may be seal the BFP popper to bonnet?
(4) My guess is that test port 1 is working if i can get the poppet go up and seal? Somebody suggested putting a spring in between retainer and puppet, will that work? I am also think about just find a fitting to cap (temporarily) the top of BFP. I don't know the size and thread and if it will work. Anybody tried that?

Please help and thanks in advance. I am kind of running out of time for this year.

If you have a drain valve upstream of the PVB, then that is always where you connect the air. Don't set the air pressure too high. 60 psi is enough. Close the PVB outlet valve, apply air until the poppet seals, let the pressure rise, then blow out a zone. Repeat this process as necessary. Don't use a small-diameter air hose. Add nipples/bushings/adapters at the compressor, so you can use a garden hose for the air.

Thanks Guys. I tried again and it worked. I had to increase PSI to about 60 initially and BFV sealed. In some cases i had to remove air hose and put it in after pressure built in. Anyway done with my 9 zone for this year. I might do it one more time over the weekend but it was nice to get as much as i could tonight as it is going to be 25 deg here, Thanks again for help.